Yes agree the discussion is about a handgun but when we start talking about 'powerful', for those who may not have experience with handguns on game and most of us won't have experience on humans, perhaps the 'powerful' is put into perspective if we can compare with rifle cartridges which most of us do know.
The 455 Webley was very effective against the natives in the early colonial days and solders in the early wars but this cartridge and others are not so effective against 'armoured' personnel as the modern soldier is now. The 357 Magnum was found to be effective in the Korean war where early armour was worn whereas the usual battle cartridges of the day were often caught short, even the venerable 45 Auto.

I've been told that the 455 Webley projectile could be stopped by a heavy army great coat worn over battle dress and a leather or webbing belt. I wouldn't like to test that out with any rifle.